Doping with impurities does what to Silicon?

In summary, when impurities are added to silicon through ion implantation, the dopant atoms initially sit at interstitial sites and are not electrically active. To activate them and change the conductivity of the silicon, a high temperature anneal is needed to allow the dopant atoms to migrate to lattice sites. This process also repairs any lattice defects caused by the ion implantation. However, if there are too many dopant atoms, the lattice strain becomes too much and defects will appear. Overall, this method allows for engineering the properties of the silicon material.
  • #1
physics.cie
17
0
I want to know ... what happens to silicon when some impurity is added to it.
Where does silicon goes??
 
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  • #2
When we doped phosphorus in site of silicon then some silicon is replaced and phosphorus is added to the site . Now I am asking for that silicon atom ??
 
  • #3
Any one here to reply
 
  • #4
They don't go anywhere, but remain in the lattice. If the doping level is small, the extra silicon atoms just get absorbed by the lattice spacing getting slightly smaller. If the doping level is large, there are typically lattice defects that absorb the extra atoms. For this reason, heavily doped junctions are always leakier than lightly doped junctions.
 
  • #5
U mean that silicon atom is now free to move in the lattice? ?
 
  • #6
No, neither the silicon atoms, nor the dopant atoms can move ... they simply make the crystal lattice "imperfect". I suppose an atom may move back and forth between two sites, especially with changes in temperature, but this is more a behavior of surface atoms which are weakly bound.

The effect of the dopant is to change the conductivity of the silicon; it also makes it N or P type: a donor of negative (electrons) or positive (holes) charges ... as with the NP diode.

In other words, it is a method of engineering the properties of the material: the dopant and the density both change the properties.
 
  • #7
physics.cie said:
U mean that silicon atom is now free to move in the lattice? ?

The usual method to introduce impurities in silicon processing is with ion implantation, where the dopant atoms are shot into the silicon crystal at high energies. If you just do the ion implantation and look at the electrical properties, most of the dopant atoms are not electrically active, since they are sitting at interstitial sites (between the silicon atoms) instead of at lattice sites. For this reason, one always follows an ion implantation with some sort of high temperature anneal, typically at least 600C. During the anneal, the dopant atoms have enough energy to move about in the lattice, and they migrate from interstitial sites to lattice sites. They then become electrically active. There is also some movement of the silicon atoms during this anneal, and lattice defects created by the ion implantation process are generally repaired, since the uniform lattice is a lower energy state. The extra atoms are taken up in the lattice by just a slight change in the lattice spacing, as I said earlier, which introduces some lattice strain. However, if there are a large number of dopant atoms, the strain gets to be too large for the lattice to sustain, and defects appear.
 

What is doping with impurities in Silicon?

Doping with impurities in Silicon is the process of intentionally adding small amounts of atoms from other elements to the Silicon crystal lattice in order to alter its electrical properties.

Why is doping with impurities done in Silicon?

Doping with impurities is done in Silicon to create either p-type or n-type semiconductors, which have different electrical properties and are used in electronic devices such as transistors and diodes.

What are the common impurities used in doping Silicon?

The most common impurities used in doping Silicon are boron, phosphorus, arsenic, and antimony. These elements are chosen because they have one extra or one less valence electron than Silicon, allowing them to create either p-type or n-type semiconductors.

How does doping with impurities affect the conductivity of Silicon?

Doping with impurities increases the conductivity of Silicon. In p-type semiconductors, the addition of impurities creates holes, which act as positive charge carriers. In n-type semiconductors, the impurities create free electrons, which act as negative charge carriers.

Can doping with impurities be reversed?

Doping with impurities can be reversed by using a process called annealing, which involves heating the doped Silicon to a high temperature. This helps redistribute the impurities and restore the original electrical properties of the Silicon crystal.

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